1. Field of the Invention
The present invention relates to a storage controller of a storage system that comprises a plurality of tape media.
2. Description of the Related Art
For example, Japanese Patent Application Laid Open No. 2004-227448 discloses technology that virtually emulates a magnetic tape medium by means of a disk device. According to this technology, files of a virtual tape are created from virtual tape storage space on the disk device and the files of the virtual tape thus created are transferred by means of a function for copying files between disk devices to the files of a virtual tape of another system.
Further, electronic data that must be archived for long periods is increasing as a result of regulations and so forth. Magnetic tape media (referred to simply as ‘tape’ hereinbelow) are considered to be more effective than disk devices from a cost perspective, for example, for archiving large-capacity data for long periods. Generally, this is because the bit cost (cost per bit) is low in comparison with that of a disk device.
Therefore, technology that installs a plurality of tapes in a storage system and provides a host device of the storage system with the plurality of tapes virtually as a plurality of disk devices maybe considered. As a result, data can be written and read to and from the tapes by accessing the virtual disk devices.
However, according to this technology, because the disk devices are virtual and the actual storage devices are tapes, there is the possibility of so-called random access occurring. Consequently, reading takes time and there is the possibility of time-out occurring in the host device. When a tape library in particular is used, it is necessary to read from the tape after loading the tape in the tape drive and positioning the tape at the object address (tape cueing), which increases the possibility of time-out.